Polycarbonate polymers are highly regarded engineering resins because of their excellent physical properties. For example, aromatic polycarbonates formed from dihydric phenols exhibit high tensile and impact strength as well as very good thermal stability. However, the use of polycarbonates in some applications, e.g., automotive, is limited somewhat because of their poor resistance to various organic solvents and other chemicals. Polycarbonates are thus blended with another thermoplastic polymer such as a polyamide in order to form a product which exhibits more chemical resistance than polycarbonate alone. For example, Japanese Kokai No. 116541/50 discloses a blend containing 80-95% by weight polycarbonate and 5-20% by weight of Nylon 12. A particularly promising combination of a polycarbonate polymer and a polyamide is disclosed in a copending and commonly assigned application, Ser. No. 939,391, filed Dec. 8, 1986. In that invention, polymers containing carbonate units in the main chain and also having functionalizing end groups are mixed with polyamides or other suitable polymers to form a thermoplastic blend in which some of the end groups of the functionalized polycarbonate polymer react with the second polymer to form a copolymer. The resulting polymer product has excellent physical properties while also exhibiting excellent chemical resistance.
The particular steps for forming the blended products disclosed in Ser. No. 939,391 include first reacting a hydroxy-terminated carbonate-containing polymer with a functionalizing agent to provide functionalized end groups on the polymer which will in turn react with the second polymer to form the copolymer.
In order to react the functionalizing agent with the thermoplastic polymer, it is generally necessary to first hydroxy-terminate the polymer. Some methods of preparing carbonate polymers terminated with hydroxy groups are known in the art. For example, U.S. Pat. No. 3,153,008, issued to D. Fox, discloses the preparation of such polymers via ester interchange during the melt polymerization of a dihydric phenol with diphenyl carbonate. However, such a melt polymerization technique has several disadvantages. For example, the technique may result in yields of hydroxy-terminated polymer which are too low for some commercial processes. Furthermore, the melt polymerization method results in a product having an excessively wide molecular weight distribution.
It is therefore an object of the present invention to provide a method of making hydroxy-terminated carbonate polymers which overcomes the foregoing disadvantages.
It is a further object of the present invention to interfacially polymerize polycarbonates of any desired molecular weight.
It is yet another object of the present invention to provide interfacially-polymerized polycarbonates having relatively narrow molecular weight ranges.
It is still another object of the invention to provide an improved chain-terminating agent for an interfacial polymerization reaction.